Because effective antiretroviral therapy substantially reduces viral load, hence the likelihood of transmission, the ultimate goal of the cascade--helping persons living with HIV (PLWH) reach undetectable viral load status--is crucial if we are to reduce forward transmission of the virus to negligible levels and, at the same time, ensure that PLWH live long and productive lives. Importantly, behavioral interventions are needed to complement and ensure the success of their biomedical counterparts at every step along the treatment cascade, whether to help a person living with HIV advance from one state of the cascade to another or to remain at the same cascade state. This application is motivated by the critical need for a uniform methodology for estimating the HIV prevention effectiveness of interventions along the HIV treatment cascade. No such methodology currently exists. HIV prevention effectiveness estimates, along with other health benefit estimates, are needed to estimate the cost-effectiveness of these interventions, and thereby to help public health decision makers select the most economically-efficient intervention for a particular purpose (e.g., linking new-diagnosed persons to care) or to choose between interventions at different stages along the cascade. We propose to refine and extend to treatment cascade interventions an existing method--based on HIV transmission rates--for estimating the number of sexually-transmitted HIV infections averted by preventive interventions, which is a necessary first step toward evaluating the cost-effectiveness of treatment cascade interventions. Uniformity is the key to making cost-effectiveness information meaningful. Only when uniform methods are used to evaluate the effectiveness of disparate interventions can the results of these analyses be compared. We believe a uniform methodology for assessing the HIV prevention effectiveness of cascade- related interventions can be developed using the concept of HIV transmission rates. Each stage of the treatment cascade is associated with a particular HIV transmission rate. The difference in transmission rates from one stage of the cascade to the next one indicates the number of HIV infections prevented, per unit time, by an intervention that helps a person living with HIV advance from the former to the latter cascade stage. The Specific Aims of the proposed research project are: (1) To conduct a thorough search of the published and grey literatures to obtain current information needed to estimate the proportionate reduction in risk associated with the transition from one state of the cascade to another; (2) Based on the empirical evidence obtained in Aim 1, to estimate the average transmission rates for stages along the HIV treatment cascade, along with plausible ranges; and (3) To assess the cost-effectiveness of two cascade interventions of demonstrated effectiveness.